I often spend many many hours remastering old tat off cassette, and I've been using
Izotope Rx2 as my tool of choice now for several years.

Prior to that I was
mostly trying to do it with Waves' de-hiss and de-hum tools, and RX2's de-hiss plugin
gives noticeably fewer artifacts.

The de-humming plugin can sometimes make
things "ring" a little (i.e. if your feed a sharp drum hit into it) - I guess that's what
inevitably happens when you fire a transient at extremely sharp notch filters...

The de-clicker sometimes misbehaves with its latency compensation in my Reaper, but I
raised a bug with Izotope and they did issue an update which cured this a bit.

I particularly like the spectral display where you can lasso little noises and attenuate
them on their own.

With all these types of plugins, I find it often pays to not
use them too aggressively in any case: your ears can get too focussed on hiss, hum and
crackles, but it's seldom necessary to remove them *entirely* - just reduce them a bit so
that the listener's ears can focus on the music... at this point, the human brain's own
clever filtering system tends to remove the hiss all by itself.

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